SALTPETRE
The attention of the ancients was naturally attracted by the
efflorescences which form on certain stones, on walls, and in caves
and cellars; and the Hindus and nomad Arabs must have noticed the
deflagration of at least one of them when a fire was lit on it. These
efflorescences consist of various salts,—sulphate and carbonate of
soda, chloride of sodium, saltpetre, &c.—but they are so similar
in appearance and taste, the only two criteria known in primitive
times,[19] that early observers succeeded in discriminating only one of
them, common salt, from the rest. So close, in fact, is the resemblance
between potash and soda, that their radical difference was only finally
established by Du Hamel in 1736. Common salt received a distinctive
name in remote times; all other salts were grouped together under such
vague generic names as _nitrum_, _natron_, _afro-nitron_, &c.
No trace of saltpetre has hitherto been found anywhere before the
thirteenth century. The Greek alchemists of preceding centuries are
silent. There is no saltpetre in the earliest recipe we possess for
Greek fire, No. 26 of the _Liber Ignium_,[20] ascribed to one Marcus
Græcus, either as given in the Paris MSS. of 1300, or in the Munich MS.
of 1438. It is true that the phrase _sal coctus_ in this recipe has
been translated by _saltpetre_ in M. Hœfer’s untrustworthy _Histoire
de la Chimie_, but as MM. Reinaud and Favé remark: “Rien n’autorise
à traduire ainsi; le sel ordinaire a été souvent employé dans les
artifices.”[21] There is no instance in Latin, I believe, of saltpetre
being designated otherwise than by _sal petræ_ (or _petrosus_), or by
_nitrum_, singly or in combination with some other word, as _spuma
nitri_. The substitution of _sal petræ_ for _sal coctus_, in later
editions of the recipe, only shows that when the valuable properties
of saltpetre became known it was employed instead of common salt.
The very fact of the change having been made by most of the later
alchemists, proves that to them _sal coctus_ did not mean _sal petræ_,
but something else. If _sal coctus_ had meant _sal petræ_, what need
was there for the change? This change, however, was not universal.
In the version of recipe 26, given in the _Livre de Canonnerie et
Artifice de Feu_, published in Paris in 1561, but written long before
by a fire-worker well acquainted with saltpetre, we find: “prenez
soufre vif, tarte, farcocoly (sarcocolla), peghel (pitch), sarcosti
(sal coctum), &c.”[22] The word _coquo_ (to boil or evaporate)
was necessarily connected with the preparation of common salt by
evaporation,[23] and _coctus_ would correctly distinguish evaporated or
artificial salt from natural or rock salt. In his “Natural History,”
xxxi. 39 (7), Pliny tells us that salt is found round the edges of
certain lakes in Sicily which are partially dried up in summer by the
heat of the sun; while in Phrygia, where much greater evaporation
takes place (_ubi largius coquitur_), a lake is dried up (and salt
is deposited) to its very middle. _Sal coctus_ was salt recovered
from salt water by natural or artificial heat, as distinguished from
natural, or rock salt, which was dug out of the ground.[24]
The Arab alchemists before the thirteenth century are as silent as the
Greeks: nothing that can be identified with saltpetre is to be found
in their voluminous works. The evidence of Geber, so often cited to
prove that saltpetre was known to the Arabs in the ninth century, has
been stripped of all authority by M. Berthelot, who has satisfactorily
proved that there were two Gebers. The real Arab, Jabir, says nothing
of saltpetre, but he mentions a salve used by naphtha-throwers[25]
as a safeguard against burns. The other Geber, or pseudo-Jabir, was
acquainted with saltpetre, as well he might be; for he was a western
who lived some time about the year 1300,[26] and wrote a number of
Latin works falsely purporting to be translations from the Arabic
of the real Jabir. All doubt about the matter has been removed by
M. Berthelot’s publication of the real Jabir’s Arabic writings.[27]
It has been also suspected that the _sal Indicus_ of the _Liber
Sacerdotum, cir._ tenth century,[28] a salt again mentioned in the
_Liber Secretorum_ of Bubacar, _cir._ 1000,[29] means saltpetre. Both
these works are translations from the Arabic or Persian,[30] and _sal
Indicus_ is the literal translation of the Persian—نمك هندي (nimaki
Hindi) = نمك سياه (nimaki siyah) = salt of bitumen; a substance of
the same family as the “salt of naphtha” also mentioned by Bubacar.
There is no word for saltpetre in classical Sanskrit, _sauverchala_
being a generic term for natural salts, which corresponded to, and
was as comprehensive as the _nitrum_, _spuma nitri_, &c., of the
West. “Recent Sanskrit formulæ for the preparation of mineral acids
containing nitre, mention this salt under the name of _soraka_. This
word, however, is not met with in any Sanskrit dictionary, and is
evidently Sanskritised from the vernacular _sora_, a term of foreign
origin.”[31] Both Professor H. H. Wilson and Professor M. Williams,
in their Sanskrit dictionaries, “erroneously render _yavakshara_ as
saltpetre, as also does Colebrooke in his ‘Amara-kosha.’”[32] The word
means impure carbonate of potash obtained by the incineration of barley
straw.[33]
At length, however, notwithstanding coarse scales and clumsy apparatus,
the want of all means of registering time and temperature, and the
absence of any general principle to guide them in their researches,
the alchemists succeeded in differentiating certain natural salts
from the rest, and among them saltpetre. The Chinese were acquainted
with it about the middle of the thirteenth century.[34] Abd Allah ibn
al-Baythar, who died at Damascus in 1248, tells us that the _flower
of the stone of Assos_ was called _Chinese snow_ by the Egyptian
physicians and _barūd_ (_i.e._ saltpetre) by the (Arab) people of
the West.[35] Friar Bacon, whose _De Secretis_ was written before 1249,
and Hassan er-Rammah who wrote 1275-95, were thoroughly acquainted
with the salt. A grand chemical discovery had been made, and saltpetre
became known from China to Spain.
The Egyptians thought fit to call saltpetre “Chinese snow,” but this
does not justify the conclusion that the discovery was made by the
Chinese. Consider our own phrases “Jerusalem” artichoke, “Welsh” onion,
and “Turkey” cock. Jerusalem is a gardener’s corruption of _girasole_,
the Turkey came from America, and the home of the Welsh onion is
Siberia. The Persians called their native alkaline salt _jamadi Chini_,
and no one will suggest that this substance came from China.
It is evident from the way in which it is mentioned by the alchemists
of the thirteenth century, and from their primitive methods of refining
it, that saltpetre was then in its infancy. Roger Bacon speaks of it
as one would speak of a substance recently discovered and still little
known—“that salt which is called saltpetre” (_illius salis qui sal
petræ vocatur_).[36] Marcus Græcus thought it necessary to explain what
the word means, in his 14th recipe which probably belongs to the latter
years of the thirteenth century.[37] The methods of refining the salt
given by Marcus and Hassan leave no possible doubt that in their time
it had but just come into use. It is true that Bacon’s method was much
superior, if the solution of his steganogram given in Chap. viii. be
accepted. But it would have been past all explanation had the method of
the greatest natural philosopher of the age been found to be no better
than that of an Arabic druggist or a European fireworker.
As the matter is one of the greatest importance, the methods of all
three are given in full, together with that of Whitehorne, 1560. The
Waltham Abbey method is added, as a standard by which to judge them. To
admit of easy comparison, the corresponding operations are marked with
the same letter. The five methods are summed up in Table I.
WALTHAM ABBEY, 1860.
A. _Preparation of grough from natural saltpetre._[38]
Natural saltpetre is dissolved in boiling water, the insoluble
impurities removed, and the solution evaporated by the sun or
artificial heat. The solid residue is grough saltpetre, and contains 1
to 10 per cent. of impurities, consisting of the chlorides of potassium
and sodium, sulphates of potash, soda, and calcium, vegetable matter,
sand, and moisture.
B. _Boiling the solution of grough saltpetre._
The grough saltpetre is placed in an open copper with a false bottom;
water is added, and heat applied until the mixture boils at 110° C.
C. _Removal of the insoluble impurities._
The scum which rises to the surface during this operation is removed by
ladles; the sand and heavy impurities fall upon the false bottom, which
is removed just before the mixture boils. The boiling is continued
until the scum ceases to rise.
D. _Second boiling of the solution._
Cold water is added; the solution is boiled for a few minutes, and then
allowed to cool somewhat.
E. _Filtration._
At 104.5° C. the mother liquid is transferred to a tank with holes in
its bottom, closed by filters.
F. _Use of wood-ash, charcoal, &c._
If the impurities prevent the liquid from passing freely through the
filters, it is treated with glue, wood-ash, or, better, with a little
animal charcoal, which seizes on the impurities and rises to the top as
scum.
G. _Crystallisation._
The mother liquid filters into the crystallising trough at 70.2° to
65.8° C.
H. _Stirring the depositing solution._
The solution is kept in constant agitation by poles whilst cooling, in
order that it may deposit in minute crystals, called _saltpetre flour_.
Large crystals contain more or less of the impure mother liquid.
I. _Washing and drying._
The agitation is discontinued at 25.8° C. and the mother liquid drawn
off. The flour is drained on an inclined plane, transferred to a
washing vat, where it is washed three times with cold water, and then
finally dried.
WHITEHORNE, 1560.
A. _Preparation of grough from natural saltpetre._
On the bottom of a vessel pierced with “three or fower littell holes”
is placed a linen cloth, “or else the end of a broom, or some straw.”
A layer of nitrified earth, “a spanne thicknesse,” is laid on this,
and on the earth “three fingers’ thicknesse” of a mixture of “two parts
of unslacked lime and three of oke asshes, or other asshes.... And so,
putting one rewe” of saltpetre alternately with one of the mixture,
“you shall fill the tubbe ... within a spanne of (its mouth), and the
rest you will fill with water.” The water, on percolating through the
mass, drips into a brass cauldron which, when two-thirds full, is
boiled “till it come to one-third part or thereabouts. And after take
it off and put it to settell in a great vessell,” when it is to be
“clarified and from earthe and grosse matter diligentlie purged.”
B. _Boiling the solution of grough saltpetre._
The solution is then “taken and boyled of new.”
F. _Use of wood-ash, animal charcoal, &c._
When the solution boils and throws up scum, it is treated with a
mixture of “3 parts of oke asshes and 1 of lime, together with 4 lbs.
of rock alum to every 100 lbs. of the mother liquid.” “In a little time
you shall see it alaie, both clear and fair and of an azure colour.”
C. _Removal of insoluble impurities._
The heavy impurities, which sink to the bottom, are got rid of by
pouring the clarified mother liquid into another vessel.
G. _Crystallisation._
“Take it out and put it in vessels of woode or of earth that are rough
within, with certain sticks of wood, to congeal.”
I. _Washing and drying._
“This same saltpeter being taken from the sides of the vessel where
it congealed, and in the water thereof washed, you must lay it upon a
table to drie throughly.”
F´.[39] _Use of wood-ash, animal charcoal, &c._
“Minding to have (saltpetre) above the common use, for some purpose,
more purified, &c. (which for to make exceeding fine powder, or aqua
fortis, is most requisite so to be):—take of the aforesaid mixture (F)
... and for every barrel of water you have put in the cauldron ... you
must put into it five potfulls” of the mixture. “In the same quantity
of water so prepared, put so much saltpeter as it will dissolve.”
D. _Second boiling of the solution._
Boil the whole until it “resolve very well.”
E. _Filtration._
When the scum rises, transfer the mother liquid to a tub with holes in
the bottom, on which is laid a linen cloth covered with a layer of
sand four finger-breadths deep.
D´. _Third boiling of the solution._
The filtered liquid is boiled again “in order to make the greater part
of the water seeth away.... Make it boil so much until you see it ready
to thicken, pouring in now and then a little of the mixture” (F).
G´. _Final crystallisation._
The mother liquid is then transferred to wooden troughs “to congeal,”
for which three or four days are allowed. “After this sort thou shalt
make the saltpeter most white and fair, and much better than at the
first setting.”
“LIBER IGNIUM,” _cir._ 1300.
A. _Preparation of grough from natural saltpetre._
If natural saltpetre is dissolved in boiling water, cleansed, and
passed through a filter, and boiled for a day and a night; the (grough)
saltpetre will be found deposited in crystals at the bottom of the
vessel.
The original is as follows:—
“Nota, quod sal petrosum est minera terræ et reperitur in scrophulis
contra lapides. Hæc terra dissolvitur in aqua bulliente, postea
depurata et distillata per filtrum et permittatur per diem et noctem
integram decoqui, et invenies in fundo laminas salis conielatas
cristallinas.”[40]
HASSAN ER-RAMMAH, 1275-95.
A. _Preparation of grough from natural saltpetre._
“Take white, clean, bright (natural) saltpetre _ad lib._, and two new
(earthen) jars. Put the saltpetre into one of them, and add some water.
Put the jar on a gentle fire until it gets warm” (and the saltpetre
dissolves. Skim off) “the scum that rises” (and) “throw it away. Stir
up the fire until the liquid becomes quite clear. Then pour it into the
other jar in such a way that no scum remains attached to it. Place this
jar on a low fire until the contents begin to coagulate. Then take it
off the fire, and beat (the crystals) gently.”
F. _Use of wood-ash, animal charcoal, &c._
“Take dry willow wood, burn it, and plunge it into water according to
the recipe for its incineration. Take three parts by weight of the
saltpetre” (just obtained), “and the third of a part of the wood-ash,
which has been carefully pulverised, and put the mixture into a jar—if
made of brass, so much the better.”
B. _Boiling the solution of grough saltpetre._
“Add water and apply heat, until the ashes and saltpetre no longer
adhere together. Beware of sparks.”
The original is as follows:—[41]
باب
صثة حل البارود
يوخذ البارود الابيض النقى النارى مهما اردت وتاخذ
طاجنين جدد ويحط فى الطاجن الواحد ويغمر بالماء ويوقد
عليه نار لينة حتى يفتر وتطلع رغوته فارمها واوقد تحته جيدا
حتى يروق ماؤه الى غاية ويقلب الماء الرايق قى طاجن اخر
بحيث لا يتراك من التفل شى ويوخذ عليه وقدا لطيفا الى
ان يجمد وتشيله وتصحنه ناعما ويوخذ الحطب الصفصاف
اليابس يحرق ويغمر على صفة الحراق ويزن من البارود
الثلثين والثلث من رماد الفحع الذى صحنته بالميزان ويعاد
الى الطاجنين وان كانت الاعادة فى طاجن نحاس فهو اجود
ويعمل عليه قليل ماء وتحمصه بحيث ان لا يلتزق واحذو من
شرر النار
ROGER BACON, _cir._ 1248.
A. _Preparation of grough from natural saltpetre._
Carefully wash the natural saltpetre, and (as far as possible) remove
all impurities. Dissolve it in water over a gentle fire, and boil it
until the scum ceases to rise, and it is purified and clarified. Let
the operation be repeated again and again, until the solution is clear
and bright. Let it then deposit its crystals of the stone which is not
a stone,[42] and dry them in a warm place.
B. _Boiling the solution of grough saltpetre._
Pulverise the crystals of grough saltpetre thus obtained, and immerse
them in water. Make a powder of two purifying substances in the
proportion of 3:2. Dissolve the crystals over a gentle fire.
F. _Use of wood-ash, charcoal, &c._
To the powder add some animal charcoal, and thoroughly incorporate the
ingredients (in a vessel). Then pour the hot solution upon it, and your
object (of clarifying the mother liquid) will be gained.
C. _Removal of the insoluble impurities._
If (by its appearance and taste you judge that) the solution is good,
pour it out (into a crystallising vessel, leaving the heavy impurities
behind).
G. _Crystallisation._
(The mother liquid is now allowed to crystallise.)
H. _Stirring the depositing solution._
(While depositing), stir the solution with a pestle. Collect the
crystals as best you can, and gradually draw off the mother liquid.
The original is as follows:—
Calcem diligenter purifica, ut fiat terra pura penitus liberata ab
aliis elementis. Dissolvatur in aqua cum igne levi, ut decoquatur
quatenus separetur pinguedo sua, donec purgatur et dealbetur. Iteretur
distillatio donec rectificetur: rectificationis novissima signa sunt
candor et crystallina serenitas. Ex hac aqua materia congelatur. Lapis
vero Aristotelis, qui non est lapis, ponitur in pyramide in loco calido.
Accipe lapidem et calcina ipsum. In fine parum commisce de aqua dulci;
et medicinam laxativam compone de duabus rebus quarum proportio melior
est in sesquialtera proportione. Resolve ad ignem et mollius calefac.
Mixto ex Phœnice adjunge, et incorpora per fortem motum; cui si liquor
calidus adhibeatur, habebis propositum ultimum. Evacuato quod bonum
est. Regyra cum pistillo, et congrega materiam ut potes, et aquam
separa paulatim.[43]
TABLE I.
_Methods of Refining Saltpetre._
+---------------------------+---+---+---+---+---+---+----+---+---+----+----+
| Roger Bacon, _cir._ 1248 | A | B | F | C | G | H |... |...|...|... |... |
| Hassan er-Rammah, | | | | | | | | | | | |
| 1275-95 | A | F | B |...|...|...|... |...|...|... |... |
| Liber Ignium, _cir._ 1300 | A |...|...|...|...|...|... |...|...|... |... |
| Whitehorne, 1560 | A | B | F | C | G | I | F´ | D | E | D´ | G´ |
| Waltham Abbey, 1860. | A | B | C | D | E | F | G | H | I |... |... |
+---------------------------+---+---+---+---+---+---+----+---+---+----+----+
A = Preparation of grough from natural saltpetre.
B = Boiling the solution of grough saltpetre.
C = Removal of insoluble impurities.
D = Second boiling of the solution.
E = Filtration.
F = Use of wood-ash, animal charcoal, &c.
G = Crystallisation.
H = Stirring the depositing solution.
I = Washing and drying.
The simple and highly probable conclusion to be drawn from the foregoing
facts is, that saltpetre was not discovered until the second quarter
of the thirteenth century; but this conclusion is not universally
accepted. It is said by some that although saltpetre was unknown to the
rest of the world until then, it had been secretly used by the Greeks
for five hundred years. This theory will be examined in the following
chapter.